Re: [PATCH v3 1/3] PCI: apple: Follow the PCIe specifications when resetting the port
From: Robin Murphy <robin.murphy@arm.com>
Date: 2021-11-24 12:58:36
Also in:
linux-pci, lkml
On 2021-11-23 18:06, Marc Zyngier wrote:
quoted hunk ↗ jump to hunk
While the Apple PCIe driver works correctly when directly booted from the firmware, it fails to initialise when the kernel is booted from a bootloader using PCIe such as u-boot. That's beacuse we're missing a proper reset of the port (we only clear the reset, but never assert it). The PCIe spec requirements are two-fold: - #PERST must be asserted before setting up the clocks, and stay asserted for at least 100us (Tperst-clk). - Once #PERST is deasserted, the OS must wait for at least 100ms "from the end of a Conventional Reset" before we can start talking to the devices Implementing this results in a booting system. Fixes: 1e33888fbe44 ("PCI: apple: Add initial hardware bring-up") Acked-by: Pali Rohár <pali@kernel.org> Signed-off-by: Marc Zyngier <maz@kernel.org> Cc: Alyssa Rosenzweig <redacted> Cc: Lorenzo Pieralisi <redacted> Cc: Bjorn Helgaas <bhelgaas@google.com> --- drivers/pci/controller/pcie-apple.c | 10 ++++++++++ 1 file changed, 10 insertions(+)diff --git a/drivers/pci/controller/pcie-apple.c b/drivers/pci/controller/pcie-apple.c index 1bf4d75b61be..957960a733c4 100644 --- a/drivers/pci/controller/pcie-apple.c +++ b/drivers/pci/controller/pcie-apple.c@@ -539,13 +539,23 @@ static int apple_pcie_setup_port(struct apple_pcie *pcie, rmw_set(PORT_APPCLK_EN, port->base + PORT_APPCLK); + /* Engage #PERST before setting up the clock */ + gpiod_set_value(reset, 0);
FWIW, given that getting the GPIO with GPIOD_OUT_LOW should have had this effect in the first place, if this isn't a no-op at this point then it would hint at something being more significantly wrong down at the GPIO/pinctrl end :/ Once you fix the polarity in the later patch, though, adding the explicit reset assertion here does seem a far nicer option than fiddling the flags to preserve the implicit assertion earlier. Cheers, Robin.
+
ret = apple_pcie_setup_refclk(pcie, port);
if (ret < 0)
return ret;
+ /* The minimal Tperst-clk value is 100us (PCIe CMS r2.0, 2.6.2) */
+ usleep_range(100, 200);
+
+ /* Deassert #PERST */
rmw_set(PORT_PERST_OFF, port->base + PORT_PERST);
gpiod_set_value(reset, 1);
+ /* Wait for 100ms after #PERST deassertion (PCIe r2.0, 6.6.1) */
+ msleep(100);
+
ret = readl_relaxed_poll_timeout(port->base + PORT_STATUS, stat,
stat & PORT_STATUS_READY, 100, 250000);
if (ret < 0) {_______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel